1. Field of the Invention
The present invention relates to a method of manufacturing a light emitting device containing light emitting elements fanned on a substrate, in which locations of short circuits between cathodes and anodes are detected and then repaired. Further, the present invention relates to a method of manufacturing a light emitting device in which locations of short circuits are detected, and then repaired, in a light emitting module wherein an IC is mounted to a light emitting panel manufactured by sealing light emitting elements formed on a substrate, using a sealing substrate. Note that the terms light emitting panel and light emitting module are generic names for light emitting devices throughout this specification. In addition, a thin film formation device capable of manufacturing a light emitting device by detecting the aforementioned short circuit locations and then repairing them is contained within the present invention.
2. Description of the Related Art
A light emitting element has high visibility because they emit light by itself, and is optimal for making a light emitting device thin because there is no need for a back light which is not necessary for a liquid crystal display device, and there is no limitation on the field of view. Light emitting devices using light emitting elements have therefore drawn attention recently as substitutes for CRTs and LCDs.
A light emitting element has a layer containing an organic compound in which electro luminescence (luminescence generated by the application of an electric field) is obtained (hereafter referred to as an organic compound layer), an anode, and a cathode. Two types of light emission exist in organic compound luminescence, light emission when returning to a ground state from a singlet excitation state (fluorescence), and light emission when returning to a ground state from a triplet excitation state (phosphorescence), and the method of detecting and then fixing short circuit locations of the present invention is applicable to both of light emitting devices employing each of light emissions.
Note that all layers formed between an anode and a cathode are defined as organic compound layers within this specification. Specifically, layers such as light emitting layers, hole injecting layers, electron injecting layers, hole transporting layers, and electron transporting layers are included as organic compound layers. Light emitting elements basically have a structure in which an anode, a light emitting layer, and a cathode are laminated in order. In addition to this structure, the light emitting elements may take other structures such as one in which an anode, a hole injecting layer, a light emitting layer, and a cathode are laminated in order, and one in which an anode, a hole injecting layer, a light emitting layer, an electron transporting layer, and a cathode layer are laminated in order.
Further, elements formed by an anode, an organic compound layer, and a cathode are referred to as light emitting elements within this specification.
Light emitting elements are formed by forming an organic compound layer between an anode and a cathode. Electrons are injected to the organic compound layer from the cathode, and holes are injected from the anode to the organic compound layer, if a voltage is applied to the electrodes of the light emitting elements.
The organic compound forming the organic compound layer then emits light in accordance with energy generated by recombination of electrons and holes in the organic compound layer.
However, if there are defects in a portion of the organic compound layer due to any reason, then short circuits occur between the cathode and the anode, and a leak current flows in the short circuit locations. Therefore, the light emitting element stops emitting light.
Reasons for defects in the organic compound layer include a case where the organic compound layer may not be formed uniformly by such that the surface of one electrode, formed prior to the formation of the organic compound layer, is not made level. In addition, there is a case in which the organic compound layer may not be formed enough on the electrode because there is dust on the electrode. If another electrode is formed on the organic compound layer having defect locations, then short circuits will occur between the cathode and the anode in portions at which the organic compound layer is not formed (defect locations).
A simple cross sectional view of a light emitting element 1104 is shown in FIG. 10A. An organic compound layer 1102 is formed on an anode 1101, and a cathode 1103 is formed on the organic compound layer 1102, forming the light emitting element 1104. Note that if a portion of the organic compound layer 1102 has a defect portion 1105 in the light emitting element 1104, then short circuits occur because the anode 1101 is contacted with the cathode 1103 in the defect portion 1105 when forming the cathode 1103 on the organic compound layer 1102.
Note that, throughout this specification, the locations at which two electrodes contact in the defect portions in the organic compound layer 1102 is referred to as the defect portion 1105, compared with a normal portion 1106 having the organic compound layer between the two electrodes.
The light emitting element 1104 normally emits light when an electric power source voltage is applied from an external electric power source 1107.
A case in which the light emitting element 1104 does not have the defect portion 1105 namely, a case in which the light emitting element 1104 only has the normal portion 1106 of FIG. 10A is shown in FIG. 10B. If an electric power source voltage Eori from the external power source 1107 is applied, then a voltage Edio is applied to the light emitting element 1104. Note that a wiring resistance is denoted by reference symbol Rwir at this time, and that a voltage applied to a wiring is denoted by reference symbol Ewir.
In contrast, a case in which the light emitting element 1104 has the defect portion 1105 shown in FIG. 10A is shown in FIG. 10C. If the voltage Eori is applied from the external electric power source 1107, then the voltage applied to the normal portion 1106 becomes E′dio, smaller than the voltage Edio shown in FIG. 10B. This is because a voltage drop occurs in the wiring in accordance with an electric current Idef flowing in the defect portion 1105, and because the wiring voltage drops from Ewir to E′wir.
Note that light is emitted in the organic compound layer when an electric current Iori flows in the organic compound layer after a forward bias is applied to both of the electrodes of the light emitting element. The light emitting element does not emit light in a case in which more electric current flows in the defect portions than in the organic compound layer.
In other words, the electric current Idio hardly flows in the normal portions i because most of the current flows in the defect portions when a forward bias is applied to a light emitting element containing a defect portion. This causes light emitting elements that have defect portions to emit light at a lowered brightness, or to turn off altogether, because it becomes difficult for electric current to flow in the organic compound layer.
Note that, in addition to the lowered brightness of the light emitting element or zero light emission therefrom, electric current always flows in the defect portion, and this promotes deterioration of the organic compound layer in the periphery of the defect portion if there is a short circuit in the defect portion.
Furthermore, the turn off of the light emitting element due to the defect portion 1105 induces the problem of a reduction in the display brightness in a pixel portion in which a plurality of pixels each having a light emitting element are formed. There is also a problem in that the electric power consumption is increased along with the occurrence of a leak current.